that
part of the annular lobe which forms the hood (m in figs. 2 and 3).

i, Superior ophthalmic tentacle.

k, Inferior ophthalmic tentacle.

l, Eye.

m, Paired laminated organ on each side of the base of the inner
inferior lobe (d) of the female.

n, Olfactory lamellae upon the inner inferior lobe (in the female).

o, The siphon (mid-foot).

p, The spadix (in the male), the hectocotylized portion of the left
inner lobe of the fore-foot representing four modified tentacles,
eight being left unmodified.

q, The anti-spadix (in the male), being four of the twelve tentacles
of the right inner lobe of the fore-foot isolated from the remaining
eight, and representing on the right side the differentiated spadix
of the left side. The four tentacles of the anti-spadix are set,
three on one base and one on a separate base.]

In the adult male nautilus we find the following important differences
in the tentaculiferous disk as compared with the female (see upper
drawing in fig. 6). The inner inferior lobe is rudimentary, and
carries no tentacles. It is represented by three groups of lamellae
(d), which are not fully exposed in the drawing. The right and left
inner lobes are subdivided each into two portions. The right shows a
larger portion carrying eight tentacles, and smaller detached groups
(q) of four tentacles, of which three have their sheaths united whilst
one stands alone. These four tentacles may be called the
"anti-spadix." The left inner lobe shows a similar larger portion
carrying eight tentacles, and a curious conical body behind it
corresponding to the anti-spadix. This is the "spadix." It carries no
tentacles, but is terminated by imbricated lamellae. These lamellae
appear to represent the four tentacles of the anti-spadix of the right
internal lobe, and are generally regarded as corresponding to that
modification of the sucker-bearing arms of male Dibranchiate
Siphonopods to which the name "hectocotylus" is applied. The spadix is
in fact the hectocotylized portion of the fore-foot of the male
nautilus. The hectocotylized arm or lobe of male Dibranchiata is
connected with the process of copulation, and in the male nautilus the
spadix has probably a similar significance, though it is not possible
to suggest how it acts in this relation. It is important to observe
that the modification of the fore-